1. Field of the Invention:
The invention in general relates to current switching such as in electromagnetic parallel rail launchers and particularly to one which reduces commutation switching energy loss.
2. Description of the Prior Art:
An electromagnetic launcher basically consists of a power supply and two generally parallel electrically conducting rails between which is positioned an electrically conducting armature. Current from the power supply flows down one rail, through the armature and back along the other rail whereby a force is exerted on the armature to accelerate it, and a payload, so as to attain a desired muzzle or exit velocity. Current conduction between the parallel rails may also be accomplished by an armature in the form of a plasma or arc which creates an accelerating force on the rear of a sabot which in the bore length supports and accelerates the projectile.
In one common type of electromagnetic launcher, the power supply is comprised of a direct current homopolar generator in series with an inductive energy storage device. A firing switch is electrically connected to short the breech end of the electrically conducting rails and is in series with the power supply.
Prior to firing a projectile, the rotor of the homopolar generator is driven to a desired rotational speed at which point, with the firing switch in the closed position, current flow is established through the storage inductor. When the current through the inductor reaches a predetermined firing level, the firing switch is opened to commutate current into the projectile launching rails.
The firing switch must provide, in the closed position, a low resistance path for current flow during the charging of the storage inductor and must thereafter, in a time interval of typically less than 1 millisecond, commutate the current flow into the conducting rails.
Typical electromagnetic launchers operate at peak current magnitudes on the order of several hundred thousand to several million amperes. In the current commutation operation, somewhere in the order of 1 to 2% of the inductively-stored energy is dissipated in arcing at the firing switch contacts by the as yet non-commutated fraction of the current. The commutation or injection of current into the rails is driven by the resulting switch arc voltage, however, the arcing results in serious switch contact melting and insulating material loss such as to severely limit the useful life of the firing switch.
It is an object of the present invention to provide a commutation arrangement wherein the switch arcing energy dissipation and arcing duration are decreased so as to significantly increase switch longevity.